This invention relates to improvements in the bonding of metal substrates to similar or dissimilar substrates. More particularly, the invention is directed to metal to metal or metal to rubber bonding using as a primer certain uniform, ultra-thin coatings prepared in situ by sol-gel processing.
In the adhesive bonding of metal to metal or rubber to metal, a primer is usually required so as to insure the formation of a strong adhesive bond. Furthermore, in many applications the primers must also confer corrosion protection. In yet other applications, the primers must be sufficiently flexible to accommodate metal forming operations without loss of metal to primer adhesion, environmental resistance, thermal or chemical degradation and anodic or cathodic deterioration. In formulating primer compositions which possess the foregoing properties, the formulator must also consider the requirements that the primer must not only form a strong adhesive bond with the final or cover coating but also enhance the bonding between the adhesive and the metal.
Silane-based adhesion promoters are commonly employed in the prior art as primers in metal to metal or metal to rubber adhesive bonding. Unfortunately, these silane-based adhesion promoters fail to provide corrosion protection at or under the bond line unless the metal surface(s) is first pre-treated as by anodizing, phosphatizing, alodizing and the like. Corrosion prevention at the bond line is desirable inasmuch as it leads to enhanced environmental resistance.
It is an object of the invention, therefore, to bond metal substrates to similar or dissimilar substrates using a primer coating that provides increased primary adhesion and environmental resistance when used with commercial adhesives.
Another object of the invention is to provide adhesively-bonded assemblies of metal to similar or dissimilar substrates whose adhesive bonds exhibit strong resistance to corrosion, heat, water, humidity and chemicals.
A further object of the invention is to provide primers for the bonding of metal to similar or dissimilar substrates which provide enhanced primary adhesion and corrosion protection at or under the bond line without the necessity of first pre-treating the metal surface.